Lithium secondary battery

Abstract

A lithium secondary battery includes a cathode including a cathode current collector, an upper cathode active material layer disposed on a top surface of the cathode current collector and a lower cathode active material layer disposed under a bottom surface of the cathode current collector, and an anode facing the cathode. A thickness of the upper cathode active material layer increases in a direction from one end portion to the other end portion of the cathode current collector, and a thickness of the lower cathode active material layer decreases in the direction from the one end portion to the other end portion of the cathode current collector.

What is claimed is: 
     
         1 . A lithium secondary battery, comprising:
 a cathode comprising a cathode current collector, an upper cathode active material layer disposed on a top surface of the cathode current collector, and a lower cathode active material layer disposed under a bottom surface of the cathode current collector; and   an anode facing the cathode,   wherein a thickness of the upper cathode active material layer increases in a direction from one end portion to the other end portion of the cathode current collector, and a thickness of the lower cathode active material layer decreases in the direction from the one end portion to the other end portion of the cathode current collector.   
     
     
         2 . The lithium secondary battery of  claim 1 , wherein a ratio of a thickness of the upper cathode active material layer disposed on the other end portion of the cathode current collector relative to a thickness of the upper cathode active material layer disposed on the one end portion of the cathode current collector is from 1.2 to 1.6, and
 a ratio of a thickness of the lower cathode active material layer disposed under the one end portion of the cathode current collector relative to a thickness of the lower cathode active material layer disposed under the other end portion of the cathode current collector is from 1.2 to 1.6.   
     
     
         3 . The lithium secondary battery of  claim 1 , wherein a sum of thicknesses of the upper cathode active material layer and the lower cathode active material layer is uniform throughout an entire region of the cathode. 
     
     
         4 . The lithium secondary battery of  claim 1 , wherein a slope angle of an extension direction of the cathode current collector with respect to a length direction of the cathode is from −2.0° to −0.1°. 
     
     
         5 . The lithium secondary battery of  claim 1 , wherein the anode comprises an anode current collector, an upper anode active material layer disposed on a top surface of the anode current collector, and a lower anode active material layer disposed under a bottom surface of the anode current collector, and
 a thickness of the upper anode active material layer decreases in a direction from one end portion to the other end portion of the anode current collector, and a thickness of the lower anode active material layer increases in the direction from one end portion to the other end portion of the anode current collector.   
     
     
         6 . The lithium secondary battery of  claim 5 , wherein the one end portion of the anode current collector overlaps the one end of the cathode current collector in a thickness direction, and the other end portion of the anode current collector overlaps the other end portion of the cathode current collector in the thickness direction. 
     
     
         7 . The lithium secondary battery of  claim 5 , wherein a sum of a thickness of the lower cathode active material layer disposed under the one end portion of the cathode current collector and a thickness of the upper anode active material layer disposed on the one end portion of the anode current collector is equal to a sum of a thickness of the upper cathode active material layer disposed on the other end portion of the cathode current collector and a thickness of the lower anode active material layer disposed under the other end portion of the anode current collector. 
     
     
         8 . The lithium secondary battery of  claim 5 , wherein a sum of thicknesses of the upper anode active material layer and the lower anode active material layer is uniform throughout an entire region of the anode. 
     
     
         9 . The lithium secondary battery of  claim 5 , wherein a ratio of a thickness of the upper anode active material layer disposed on the one end portion of the anode current collector relative to a thickness of the upper anode active material layer disposed on the other end portion of the anode current collector is from 1.2 to 1.6, and
 a ratio of a thickness of the lower anode active material layer disposed under the other end portion of the anode current collector relative to a thickness of the lower anode active material layer disposed under the one end portion of the anode current collector is from 1.2 to 1.6.   
     
     
         10 . The lithium secondary battery of  claim 5 , wherein a slope angle of an extension direction of the anode current collector with respect to a length direction of the anode is from 0.10 to 2.0°. 
     
     
         11 . The lithium secondary battery of  claim 1 , wherein the upper cathode active material layer and the lower cathode active material layer include different types of cathode active materials. 
     
     
         12 . The lithium secondary battery according to  claim 1 , wherein the lithium secondary battery has a uniform thickness throughout an entire region.